Checking a few instruction manuals, different Host/Client combinations seem to use all the options from full CRC, to XOR checksum, to completely ignoring the checksum/CRC altogether.

The way the protocol is supposed to work is that the host will inquire if the client supports CRCs, if so then it uses them. If not it is supposed to fall back to a Checksum. Even with a checksum, there is no law saying that the host needs to pay attention, so apparently some don’t. The standard way of responding to a bad CRC/Checksum response is to resend the record. This is much quicker than resending the whole file like the “Verify” flag does.

Not the point. The point was whether or not the article SAID it did. The article DOES say that it does. Nowhere was Optiboot mentioned. Maybe Optiboot doesn’t, don’t know, but again, that never was the point.

Also, quoting the Omimex manual for Sparkfuns STK500 Compatible USB Programmer: “Boot loader implements the standard protocol XMODEM with CRC16 for firmware update.” The Atmel manual states that it uses a checksum on each record sent, both are options for the Xmodem protocol. Completely ignoring the checksum/CRC response is also an option, but not recommended.

Any competent Xmodem host will resend a record if the client responds that the checksum/CRC failed. Program downloaders have been routinely doing this since the ‘70s. If Optiboot doesn’t, it certainly should!

Your numbers are only good for constant acceleration, and with no friction. Fuel burns, rocket gets lighter, a=F/m so acceleration goes up (and the integral gets more complicated). Also, many solid fuel rockets are burned in a way where the burning surface area increases during the burn. So not only does m decrease, but also F increases, sometimes by many multiples. Low sub-sonic air friction increases approx with the square of velocity, but decreases with altitude. Super and trans-sonic friction is not so simple. Can’t do those numbers in my head anymore, but I suspect that they’re different than what you got. Just sayin'.

Not a flame, just the facts. The original poster noted the declining quality of many current ‘data-sheets’. I am simply agreeing, with recent examples.<br />
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NC, no connection, means, and has meant for many years, no - decades, that there is No Connection to circuitry inside the chip. One of the examples I gave went further to expand the definition as “No internal Connection” and “these may be driven or left floating”. To distort this to mean that you should not make any connection to this point defies logic. <br />
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There are a wide variety of other terms that are available for “Do Not Connect”, “Do Not Use”, “For Testing Only”, etc. Perhaps the examples I gave could have used “/Power-Supply Shutdown” on one, and “Vcc” for the others, rather than “NC”.<br />
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It is apparent that many of the people who are writing these ‘data-sheets’ don’t consider them important enough to even turn on the spell-checker, much less actually insure that the information is accurate. <br />
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In any writing, it is important to write in a way that is easy to understand. In technical writing it is important to write in a way that is difficult to mis-understand. Technical writing is an art, an art that many people simply do not have.<br />
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jdf2525 “I don’t know if it’s just that I’m getting old and cantankerous”<br />
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Oh! Don’t get me started… It’s not just you. I’ve just about given up on even spending the time to read data-sheets. I recently made a board with 3 different chips that the data-sheets didn’t know what NC means. It means, and has meant for many years, No Connection. It does not mean <br />
“don’t connect or else things will blow up.” <br />
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One, a 12A switching supply (2 on the board), had 3 pins (out of 133 in an LGA package) to be used to reinforce the physical mounting. These were further explained as “no internal connection”. This was true for 2 of the 3, the third pin forcefully shut down the output. How long did it take me to find that? when the LGA pins are under the chip on a 12 layer board? when the data-sheet explicitly says “no internal connection”?<br />
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Another, a Flash memory, went even further to state that the NC pins could be driven or left floating. As per normal human practices, these pins were merged into the ground plane, along with several interspersed labeled ground pins. The only thing is, two of these NC pins were actually unlabeled VCC pins, resulting in a direct short through the chip to the ground plane. How long did it take to find that?…<br />
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Another chip on this board, a 1517 pin (not a typo!) BGA, had one set of pins labeled NC, and another labeled DNU (Do Not Use). Do you think I am going to believe what the data-sheet actually says as I wire up a $4000 chip? <br />
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Timing diagrams are even worse. Polarity matters! Phase relationship matters! TIMING matters! That is why it is called a timing diagram. The information provided in some ‘timing diagrams’ is completely un-helpful. Pretty pictures… yeah, I get it, you can work “Paint” or something similar. A pencil scribble drawing with correct information would be much more useful.<br />
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The data-sheet is supposed to be so that you don’t have to get a chip, breadboard it, and randomly try wires and interface circuitry till you can get it to work. Instead, all too often today’s data-sheets are created by people who really don’t care. Standards aren’t what is needed. What is needed are people who care, and who have at least half a clue.

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